A fluorescent lamp (also called a fluorescent tube) uses electrical current to excite a vapor within a glass tube resulting in the discharge of electrons. Visible light is produced when the electrons cause a material coating the inner wall of the glass tube to fluoresce. Linear fluorescent lamps are routinely used in commercial or institutional buildings, and are commonly installed in troffer light fixtures (recessed troughs installed in a ceiling) and pendant light fixtures (housings suspended from a ceiling by a chain or pipe).
Fluorescent lamps have been steadily replacing incandescent lamps in many lighting applications. Compared to an incandescent lamp, a fluorescent lamp converts electrical power into useful light more efficiently, delivers a significantly longer useful life, and presents a more diffuse and physically larger light source. However, fluorescent lamp technology has disadvantages. A fluorescent lamp is typically more expensive to install and operate than an incandescent lamp because the fluorescent lamp requires a ballast to regulate the electrical current. Fluorescent light fixtures cannot be connected directly to dimmer switches intended for incandescent lamps, but instead require a compatible dimming ballast. The performance of fluorescent lamps may be negatively impacted by environmental conditions such as frequent switching and operating temperatures. Many fluorescent lamps have poor color temperature, resulting in a less aesthetically pleasing light. Some fluorescent lamps are characterized by prolonged warm-up times, requiring up to three minutes before maximum light output is achieved. Also, if a fluorescent lamp that uses mercury vapor is broken, a small amount of mercury (classified as hazardous waste) can contaminate the surrounding environment.
Digital lighting technologies such as light-emitting diodes (LEDs) offer significant advantages over traditional linear fluorescent lamps. These include but are not limited to better lighting quality, longer operating life, and lower energy consumption. Increasingly, LEDs are being designed to have desirable color temperatures. Moreover, LEDs do not contain mercury. Consequently, a market exists for LED-based retrofit alternatives to legacy lighting fixtures that use fluorescent lamps. However, a number of installation challenges and costs are associated with replacing linear fluorescent lamps with LED illumination devices. The challenges, which are understood by those skilled in the art, include light output, thermal management, and ease of installation. The costs, which are similarly understood by those skilled in the art, typically stem from a need to replace or reconfigure a troffer or pendant fixture configured to support fluorescent lamps to support LEDs instead.
By the very nature of their design and operation, LEDs have a directional light output. Consequently, the light emitted by an LED may not have the nearly omni-directional and uniform light distribution of incandescent and fluorescent lamps. Although multiple LEDs can be used in a single lamp, lighting solutions employing LEDs do not have light distribution properties approximating or equaling the dispersion properties of traditional lamps.
Another challenge inherent to operating LEDs is heat. Thermal management describes a system's ability to draw heat away from the LED, either passively or actively. LEDs suffer damage and decreased performance when operating in high-heat environments. Moreover, when operating in a confined environment, the heat generated by an LED and its attending circuitry itself can cause damage to the LED. Heat sinks are well known in the art and have been effectively used to provide cooling capacity, thus maintaining an LED-based light bulb within a desirable operating temperature. However, heat sinks can sometimes negatively impact the light distribution properties of the light fixture, resulting in non-uniform distribution of light about the fixture.
Power supply requirements of LED-based lighting systems can complicate installation of LEDs as a retrofit to existing light fixtures. LEDs are low-voltage light sources that require constant DC voltage or current to operate optimally, and therefore must be carefully regulated. Too little current and voltage may result in little or no light. Too much current and voltage can damage the light-emitting junction of the LED. LEDs are commonly supplemented with individual power adapters to convert AC power to the proper DC voltage, and to regulate the current flowing through during operation to protect the LEDs from line-voltage fluctuations.
A need exists for a troffer-retrofit luminaire that may be employed within the volume of space available in an existing troffer and pendant light fixture, and that delivers improved lighting quality compared to traditional LED troffers. More specifically, a need exists for a troffer-based lighting solution that benefits from the advantages of digital lighting technology, while exhibiting better cut-off and reduced glare than legacy troffer solutions. Additionally, a need exists for a luminaire designed for ease of installation as well as for manufacturing cost reduction. The lighting industry is experiencing advancements in LED applications, some of which may be pertinent to certain aspects of replacing linear fluorescent lamps.
U.S. patent application Ser. No. 12/712,743 by Peifer et al. is directed to a troffer-style light fixture using LEDs to cross-light internal surfaces of the troffer, causing light from opposite LED modules to mix as light is emitted from the fixture. However, this cross-lighting solution still employs separate LEDs pointing generally downward. Such a design is known in the art to create bright and dark spaced spots onto an illuminated surface, and also to emit light with poor cutoff.
U.S. Pat. No. 8,038,314 to Ladewig discloses a troffer-style luminaire having an interior region defined by two sides and a top extending between the sides. Indirect LEDs are coupled along interior surfaces of the sides, within the interior region. However, the luminaire is characterized by LED-support means (i.e., the interior surfaces of the sides) that are separate and distinct from thermal management means (e.g., exterior heat sink). This design adds to manufacturing cost due to material and complexity.
U.S. Pat. No. 8,297,798 to Pittman et al. discloses a lighting fixture having a reflector, a pedestal projecting through an opening substantially central to the reflector, and a lighting module mounted on the pedestal. The lighting module includes a frame and indirect LEDs that emit light toward the interior surface of the reflector. However, positioning of the lighting module obscures the reflector section opposite the frame as perceived from any point external to the luminaire.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.